1. Field
One embodiment of the invention relates to an acoustic apparatus for measuring and correcting the resonance characteristics of the outer-ear canals of a listener, to which a sound source signal is supplied from an earphone or a headphone.
2. Description of the Related Art
While listening to music through an earphone or a headphone (hereinafter, “earphone”), a listener may perceive an unnatural sound when the outer-ear canals are plugged with the earphone and resonance occurs due to interference with the sound waves reflected from the eardrums, emphasizing the sound of the resonance frequency. It is therefore desirable to measure the resonance characteristics of the outer-ear canals and to correct the resonance characteristics before the listener starts listening to music.
The shapes and acoustic transmission characteristic of outer-ear canals, and the physical properties and acoustic transmission characteristic of eardrums differ from person to person. Further, the resonance in either outer-ear canal changes in accordance with the type of the earphone and the state in which the earphone is held in the outer-ear canal. Hence, the resonance characteristics of the outer-ear canals must be measured and corrected for each earphone and each listener in order to achieve accurate measurement and correction of the resonance characteristics of the outer-ear canals.
Jpn. Pat. Appln. KOKAI Publication No. 2004-320098 describes a damping control circuit for use in earphones (see paragraph 0013). This circuit suppresses the vibration of the diaphragms of the earphone, which is pertinent to the resonance characteristics of the outer-ear canals. The damping factor becomes larger in the frequency domain of 3 to 4 kHz, where the acoustic gain of the outer-ear canals is maximal. Hence, the harmful vibration of the diaphragms of the earphone, which pertains to the resonance characteristics of the outer-ear canals, can be effectively controlled.
In the damping apparatus for use in earphones, which is disclosed in the above-identified publication, the damping factor becomes larger in the frequency domain of 3 to 4 kHz, where the acoustic gain of the outer-ear canals is maximal. The harmful vibration of the diaphragms of the earphone, which pertains to the resonance characteristics of the outer-ear canals, can therefore be effectively controlled. However, the resonance characteristics of the listener's outer-ear canals cannot be measured or corrected to accord with the vibration characteristic of the earphone.